Signal processor and signal processing method

ABSTRACT

Provided are a video signal processor and a video signal processing method. The video signal processor consists mainly of a sharpening circuit, a non-correlation detecting circuit, and a noise level detecting circuit. The sharpening circuit filters an input luminance signal using a transversal filter, multiplies the luminance signal by a predetermined factor, adjusts a time lag the luminance signal undergoes, and adds the resultant luminance signal to an original luminance signal. The non-correlation detecting circuit performs non-correlation detection to discriminate a portion of the filtered luminance signal, which contains only a noise, from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage. The noise level detecting circuit detects a noise level. When a received luminance signal portion is detected to contain only a noise, the sharpening circuit cancels the noise contained in the luminance signal portion. At this time, the threshold voltage employed in the non-correlation detection is varied depending on the detected noise level. Thus, the video signal processor and video signal processing method successfully discriminate a low-level signal from a large-amplitude noise, and reduce noises contained in a video signal.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a video signal processor to which a sharpening circuit is preferably adapted in order to improve the sharpness of a picture, and a video signal processing method implemented in the video signal processor.

[0003] 2. Description of the Related Art

[0004] A sharpening circuit is a known means that has the ability to improve sharpness when adapted to a television receiver, a video tape player, or a digital video disk player.

[0005] A noise reducing circuit for the conventional television receiver includes a circuit that improves sharpness to make a noise indiscernible. Specifically, the circuit detects a noise level, adjusts a sharpness level in inverse proportion to the detected noise level, and increases a gain to be given to a relatively high-frequency signal component.

[0006] However, as far as the foregoing conventional noise reducing circuit is concerned, if a signal contains a noise, a sharpening circuit may intensify the noise. This may lead to deterioration of image quality. For this reason, another method adopts a circuit that detects a noise level, adjusts a sharpness level in inverse proportion to the detected noise level, and thus makes a noise indiscernible. In this case, the signal-to-noise ratio of a video signal cannot be improved directly. Moreover, there is a drawback that if a noise is present, sharpness cannot be improved but deteriorates.

[0007] The sharpening function includes a core ring sharpening technology that sharpens only a signal whose level is equal to or larger than a certain level but does not sharpen small-amplitude signals including a noise. However, the core ring sharpening technology has a drawback that a noise contained in a video signal cannot be eliminated.

SUMMARY OF THE INVENTION

[0008] Accordingly, an object of the present invention is to provide a video signal processor that successfully reduces the level of a noise contained in a video signal, and a video signal processing method implemented in the video signal processor.

[0009] A video signal processor in accordance with the present invention consists mainly of a sharpening circuit and a non-correlation detecting circuit. The sharpening circuit filters a received luminance signal using a transversal filter, multiplies the filtered luminance signal by a predetermined factor, adjusts a time lag the luminance signal undergoes in the transversal filter, and adds the resultant luminance signal to an original luminance signal. The non-correlation detecting circuit performs non-correlation detection to discriminate a portion of the luminance signal filtered by the transversal filter, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation. When a received luminance signal portion is detected to contain only a noise by the non-correlation detecting circuit, the sharpening circuit performs noise canceling to subtract the noise from the luminance signal portion.

[0010] A video signal processing method in accordance with the present invention consists mainly of sharpening and non-correlation detection. During sharpening, a transversal filter is used to filter a received luminance signal, and the filtered luminance signal is multiplied by a predetermined factor. A time lag the luminance signal undergoes in the transversal filter is adjusted, and the resultant luminance signal is added to an original luminance signal. During non-correlation detection, a portion of the luminance signal filtered by the transversal filter, which contains only a noise, is discriminated from a portion thereof containing a noise and exhibits a fluctuation. When a received luminance signal portion is detected to contain only a noise during the non-correlation detection, noise canceling is performed in order to subtract the noise from the luminance signal portion during sharpening.

[0011] Moreover, a video signal processor in accordance with the present invention consists mainly of a sharpening circuit, a non-correlation detecting circuit, and a noise level detecting circuit. The sharpening circuit filters a received luminance signal using a transversal filter, multiplies the filtered luminance signal by a predetermined factor, adjusts a time lag the luminance signal undergoes in the transversal filter, and adds the resultant luminance signal to an original luminance signal. The non-correlation detecting circuit performs non-correlation detection to discriminate a portion of the luminance signal filtered by the transversal filter, which contains only a noise from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage. The noise level detecting circuit detects a noise level. When a received luminance signal portion is detected to contain only a noise by the non-correlation detecting circuit, the sharpening circuit performs noise canceling to subtract the noise from the luminance signal portion. At this time, the threshold voltage employed in the non-correlation detection by the non-correlation detecting circuit is varied depending on the noise level detected by the noise level detecting circuit.

[0012] Moreover, a video signal processing method in accordance with the present invention consists mainly of sharpening, non-correlation detection, and noise level detection. During sharpening, a transversal filter is used to filter a received luminance signal, and the filtered luminance signal is multiplied by a predetermined factor. A time lag the luminance signal undergoes in the transversal filter is adjusted, and the resultant luminance signal is added to an original luminance signal. During non-correlation detection, a portion of the luminance signal filtered by the transversal filter, which contains only a noise, is discriminated from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage. During noise level detection, a noise level is detected. Herein, when a luminance signal portion is detected to contain only a noise during the non-correlation detection, noise canceling is performed in order to subtract the noise from the luminance signal portion during sharpening. At this time, the threshold voltage employed in the non-correlation detection is varied depending on the noise level detected during the noise level detection.

[0013] Accordingly, the present invention exerts the operation described below.

[0014] According to the present invention, in a video signal processor and a video signal processing method, non-correlation detection is performed in order to discriminate a portion of a luminance signal, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation. When a received luminance signal portion contains only a noise, noise canceling is performed in order to subtract the noise from the luminance signal portion.

[0015] According to the present invention, a signal containing a noise has its sharpness improved through sharpening without deterioration of image quality while having the noise canceled.

[0016] Furthermore, according to the present invention, in a video signal processor and a video signal processing method, non-correlation detection is performed in order to discriminate a portion of a luminance signal, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation. When a received luminance signal portion contains only a noise, noise canceling is performed in order to subtract the noise from the luminance signal portion. A threshold voltage based on which a signal is discriminated from a noise is varied depending on a detected noise level. Thus, the noise level based on which a noise is subtracted from the luminance signal portion that contains only the noise is varied.

[0017] According to the present invention, even when the level of a noise varies largely, while the noise is canceled, sharpness is improved through sharpening without deterioration of image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram of the circuitry of a sharpening circuit adapted to a video signal processor in accordance with a first embodiment;

[0019]FIG. 2 is a circuit diagram showing an example of circuitry of a transversal filter included in the sharpening circuit;

[0020]FIG. 3 is a circuit diagram showing an example of circuitry of a non-correlation detecting circuit included in the sharpening circuit;

[0021]FIG. 4 is a circuit diagram showing an example of circuitry of an equalizer and adder included in the sharpening circuit;

[0022]FIG. 5 is a circuit diagram showing an example of circuitry of a delay device included in the transversal filter;

[0023]FIG. 6A to FIG. 6F are timing charts indicating actions performed by a subtraction type noise reducing circuit;

[0024]FIG. 6A shows a received luminance signal;

[0025]FIG. 6B shows a differential wave of the luminance signal;

[0026]FIG. 6C shows a subtracted signal of the differential wave of the luminance signal;

[0027]FIG. 6D shows an absolute value signal of the differential wave;

[0028]FIG. 6E shows a signal having a noise subtracted based on a threshold voltage (1 VF) or less;

[0029]FIG. 6F shows a differential wave adaptable to a low threshold voltage or a high threshold voltage;

[0030]FIG. 7 shows examples of the frequency band of the luminance signal and the passband of the transversal filter;

[0031]FIG. 8 is a flowchart describing sharpening;

[0032]FIG. 9 is a block diagram showing the circuitry of a sharpening circuit adapted to a video signal processor in accordance with a second embodiment;

[0033]FIG. 10 is a circuit diagram showing an example of circuitry of a noise level detecting circuit;

[0034]FIG. 12A to FIG. 12C show the waveforms of signals for explaining actions performed by a synchronizing separator circuit and a sampling signal generator included in the noise level detecting circuit;

[0035]FIG. 12A shows timing pulses preceding and succeeding a vertical sync signal contained in a luminance signal sent to the synchronizing separator circuit;

[0036]FIG. 12B shows one horizontal scanning period (1H) that starts at the leading edge of the vertical sync signal;

[0037]FIG. 12C shows a period during which a sampling signal is high (H); and

[0038]FIG. 13 is a circuit diagram showing an example of circuitry of a sampling signal generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] A video signal processor in accordance with a first embodiment of the present invention detects a correlation, subtracts a noise from a received signal to thus reduce the noise, and adds a sharpness component to the signal to thus improve sharpness.

[0040] The video signal processor in accordance with the first embodiment of the present invention is adapted to a television receiver in which a sharpening circuit is incorporated. The television receiver receives telecast, reduces a noise of a video signal contained in the received telecast wave, sharpens the video signal that has the noise thereof reduced, and displays a picture on a display means.

[0041] The video signal processor is not limited to the television receiver in which the sharpening circuit is incorporated. The video signal processor may be adapted to a television receiver that reduces a noise of a video signal sent from an external or built-in video signal source (video reproducing apparatus), sharpens the resultant video signal, and displays a picture according to the video signal.

[0042] The circuitry of the sharpening circuit adapted to the video signal processor in accordance with the first embodiment of the present invention will be described below. FIG. 1 shows the circuitry of the sharpening circuit adapted to the video signal processor in accordance with the first embodiment of the present invention. A luminance signal is sent to the sharpening circuit 14. The luminance signal is separated from a video signal sent to a television receiver (video signal sent from an internal tuner or sent externally) by means of a luminance/chrominance separator circuit. Alternatively, the luminance signal is a luminance signal separated from a chrominance signal included in a video signal and sent from an external video signal source.

[0043] A portion of the video signal processor in accordance with the first embodiment of the present invention, which is encircled with a dashed line in FIG. 1, is the same as a conventional sharpening circuit. A luminance signal is sent to a transversal filter 11 shown within the dashed line. The transversal filter 11 produces a sharpness component that is weighted by a variable gain amplifier 12. The weighted signal is added to the original luminance signal by an adder circuit 13. At this time, a weighting factor by which the amplifier 12 amplifies a signal is determined with, for example, user-specified data entered at a microcomputer.

[0044] If a received luminance signal contains noises, a non-correlation detecting circuit 15 discriminates a portion of the luminance signal containing only the noise from a portion thereof containing the noise and exhibiting a fluctuation. When a received luminance signal portion contains only the noise, the non-correlation detecting circuit 15 transfers a negative weighting factor to the amplifier 12. Consequently, noise canceling is performed to subtract the noise from the luminance signal.

[0045]FIG. 2 shows a practical example of the circuitry of the transversal filter 11. Referring to FIG. 2, a signal delayed by a delay device 21, a signal delayed by the delay device 21 and a delay device 22 and multiplied by a predetermined gain by an amplifier 23, and the received luminance signal are added up by an adder 24. The adder 24 produces a sharpness component.

[0046]FIG. 3 shows a practical example of the circuitry of the non-correlation detecting circuit 15 shown in FIG. 1. A signal applied to an input terminal 31 and passed through a bandpass filter (BPF) 32 (having the same characteristic as the transversal filter 11 shown in FIG. 1) is applied to one of input terminals of a differential amplifier 33 via a resistor R1. A signal that is a fraction of a supply voltage produced by resistors R2 and R3 is applied to the other input terminal of the differential amplifier 33. A resistor R4 is connected to one input terminal of the differential amplifier 33 and to an output terminal thereof through which an inverted output signal whose polarity is the opposite of an input polarity is transmitted. The differential amplifier 33 and resistors R1 to R4 act as a comparator. In this case, the threshold voltage of the comparator is determined with a ratio of a fraction of the supply voltage produced by the resistor R2 to a fraction thereof produced by the resistor R3. A voltage representing a factor entered at the microcomputer shown in FIG. 1 is applied to a node between the resistors R2 and R3.

[0047] An non-inverted output signal of the differential amplifier 33, of which polarity is the same as an input polarity, is applied to the base of a transistor Q1, and an inverted output signal thereof is applied to the base of a transistor Q2. The transistors Q1 and Q2 have emitters thereof connected to each other, whereby an emitter follower is constructed. The emitter follower detects an absolute value of an output of the differential amplifier 33. A resistor R5 is connected between the emitters of the transistors Q1 and Q2 and a ground. A node between the transistors Q1 and Q2 and the resistor R5 is connected to the base of a transistor Q3. A resistor R6 links the emitter of the transistor Q3 and the supply voltage line. A non-correlation detection signal output terminal 34 is led out from a node between the transistor Q3 and resistor R6.

[0048]FIG. 4 shows a practical example of the circuitry of the adder circuit 13 shown in FIG. 1. The adder circuit 13 shown in FIG. 4 consists mainly of an equalizer 42 for adjusting a delay and an adder 43. A luminance signal applied to the input terminal 41 of the equalizer 42 is applied to the base of a transistor Q11 included in the equalizer 42. A resistor R11 is connected between the collector of the transistor Q11 and the supply voltage line. A resistor R12 is connected between the emitter of the transistor Q11 and the ground. One terminal of a resistor R13 is connected to the emitter of the transistor Q11. One terminal of a capacitor C11 is connected to the collector of the transistor Q11. The other terminal of the resistor R13 and the other terminal of the capacitor C11 are connected to the base of a transistor Q12. A resistor R14 is connected between the transistor Q12 and the supply voltage line. A resistor R15 is connected between the emitter of the transistor Q12 and the ground. An output of the equalizer 42 is led out from a node between the transistor Q12 and resistor R14.

[0049] The transistor Q11 in the equalizer 42 serves as a delay circuit, and can adjust a minute difference of a delay time by adjusting a time constant of a capacitor-resistor circuit composed of the capacitor C11 and resistor R13. The transistor Q12 inverts an input signal and adjusts a gain to be given to the signal. An output signal of the transistor Q12 is transmitted as an output signal of the equalizer 42.

[0050] The output signal of the equalizer 42 is applied to the base of a transistor Q13 included in the adder 43. The adder 43 consists of two transistors Q13 and Q14, and resistors R16, R17, R18, and R19. Another addition signal sent from the transversal filter 11 is applied to the base of the transistor Q14 through an input terminal 44. The resistor R16 is connected between the emitter of the transistor Q13 and the ground. The resistor R19 is connected between the emitter of the transistor Q14 and the ground. A series circuit composed of the resistors R17 and R18 is connected between the emitters of the transistor Q13 and Q14. An addition signal output terminal 45 is led out from a node between the resistors R17 and R18.

[0051]FIG. 5 shows an example of circuitry for adjusting the timings of the delay devices 21 and 22 shown in FIG. 2. A signal applied to an input terminal 51 is applied to the base of a transistor Q21. A resistor R21 is connected between the emitter of the transistor Q21 and the ground. A node between the transistor Q21 and resistor R21 is connected to the input terminal of the amplifier 53 via a resistor R22 and an LC delay line 52. An output of the amplifier 53 is applied to an output terminal 54 of the delay device. The input terminal of the amplifier 53 is grounded via a resistor R23.

[0052] Since the delay devices 21 and 22 have the circuitry shown in FIG. 5, a termination resistor is connected to the LC delay line 52. A signal passed through the LC delay line 52 decays to have the level thereof halved. For compensating the decay, the amplifier 53 in the delay device shown in FIG. 5 performs amplification.

[0053] Next, actions to be performed in the subtraction type noise reducing sharpening circuit adapted to the video signal processor in accordance with the first embodiment of the present invention will be described with reference to the timing chart of FIG. 6. Actions to be performed for sharpening are identical to those to be performed by a conventional sharpening circuit, and the description of the sharpening actions will be omitted. FIG. 6A shows an example of a change in the level of a luminance signal sent to the subtraction type noise reducing sharpening circuit. The luminance signal contains a horizontal sync signal h that develops in certain cycles. The portions of the luminance signal preceding and succeeding the horizontal sync signal h are referred to as a front porch f and a back porch b respectively. The front porch f and back port b have a constant level. Video information V has a level proportional to a luminance level. Herein, assume that a noise N is superimposed on part of the video information V (the noise N is shown enhanced in the drawing).

[0054] The luminance signal is applied to the bandpass filter 32 installed in the input stage of the non-correlation detecting circuit 15. When the luminance signal has only a high-frequency component thereof passed through the bandpass filter 32, the luminance signal becomes a differential wave shown in FIG. 6B. The high-frequency component wave exhibits a fluctuation on borders between the horizontal sync signal and the front porch f and back porch b, and borders between the video information V and the front porch f and back porch b. Moreover, a noise appears.

[0055] Assuming that the signal shown in FIG. 6B is subtracted from the signal shown in FIG. 6A, the noises are canceled as shown in FIG. 6C. However, the leading and trailing edges of the horizontal sync signal are devoid of a high-frequency component. The signal shown in FIG. 6C is therefore unsuitable for a video signal. In the present embodiment, the non-correlation detecting circuit 15 is included in order to detect a non-correlation of the signal. Subtraction of the signal is controlled based on the result of detection. What is referred to as a non-correlation refers to the leading or trailing edge of a flat portion (a portion of the luminance signal whose level is constant) or any other fluctuation occurring during horizontal scanning.

[0056] Specifically, the high-frequency component wave shown in FIG. 6B is rectified to produce a wave shown in FIG. 6D. The signal level of the wave may be, as shown in FIG. 6E, lower than a threshold voltage (1 VF). When the level of a received luminance signal portion is lower than the threshold voltage, a negative factor is set in the weighting circuit, that is, the variable gain amplifier 12 included in the sharpening circuit. The weighted luminance signal portion is subtracted from an original luminance signal portion, and the succeeding luminance signal portion is treated by the adder circuit 13. The noises can therefore be subtracted. Consequently, the adder circuit 13 adds a sharpness component to the portions of a luminance signal that exhibits a fluctuation and has no correlation, that is, the borders between the horizontal sync signal and the front porch f and back porch b, and the borders between the video information V and the front porch f and back porch b. The portion of the luminance signal that exhibits no fluctuation but has a correlation has the noise subtracted therefrom.

[0057]FIG. 6F shows a wave which is drawn with a dashed line and for which the threshold voltage can be set to a lower voltage T1, and a wave which is drawn with a solid line and for which the threshold voltage can be set to a high voltage T2. The adder circuit 13 adds a sharpness component to the portions of the luminance signal that exhibit a fluctuation but have no correlation, that is, the borders between the horizontal sync signal and the front porch f and back porch b, and the borders between the video information V and the front porch f and back porch b. The portion of the luminance signal that exhibits no fluctuation and has a correlation has a noise thereof subtracted based on the low threshold voltage T1 indicated with the dashed line or the high threshold voltage T2 indicated with the solid line.

[0058]FIG. 7 shows examples of the frequency band of a luminance signal to be treated by the noise reducing sharpening circuit adaptable to the video signal processor in accordance with the present embodiment, and the passband of the transversal filter 11. The axis of abscissas indicates frequencies, and the axis of ordinates indicates gains to be given to a signal. When the frequency of a luminance signal sent to the sharpening circuit employed in the present embodiment is approximately 4 MHz, the passband of the transversal filter 11 is set to, for example, 2 MHz or higher. The bandpass filter 32 used to detect a correlation shall have a property of passing frequencies higher than a frequency slightly lower than the lower limit of the passband of the transversal filter 11. The passband of the bandpass filter 32 is made wider than that of the transversal filter 11. This is intended to reliably detect a non-correlation of a signal (a fluctuation of a luminance signal) over a wider frequency band.

[0059] Next, noise reduction performed by the noise reducing sharpening circuit adaptable to the video signal processor in accordance with the present embodiment will be described with reference to the flowchart of FIG. 8. Referring to FIG. 8, when a luminance signal is received, the transversal filter 11 limits the luminance signal to a predetermined frequency band at step S101. Concurrently, a non-correlation is detected at step S102. It is judged at step S102 of non-correlation detection whether a (great) correlation is detected. If a great correlation is detected, it is judged that the luminance signal is greatly affected by a noise. An amplification factor or a weighting factor is set to a negative value at step S105 because of the great correlation. At step S106 of addition, noise subtraction is executed.

[0060] It is judged at step S102 of non-correlation detection whether a non-correlation (little correlation) is detected. If a little correlation is detected, it is judged at step S104 that the luminance signal is little affected by a noise. At step S105, the amplification factor, that is, the weighting factor is set to a positive value because of the little correlation. At step S106 of addition, the high-frequency component of the luminance signal is added to an optical luminance signal for enhancement in order to thus improve sharpness.

[0061] The sharpening circuit adaptable to the video signal processor in accordance with the present embodiment includes a correlation detecting circuit capable of detecting a signal and a noise. A sharpness component can be reduced but will not be added to the noise that deteriorates image quality.

[0062] Moreover, in the video signal processor of the present embodiment, the microcomputer is used to enter a noise reduction rate. The noise reduction rate can therefore be changed to any value. The core ring sharpening technology may therefore be implemented in the video signal processor.

[0063] When the video signal processor of the present embodiment is used to reduce a noise contained in a received video signal, a white noise deriving from a feeble electric field can be reduced successfully.

[0064] Next, a description will be made of a video signal processor in accordance with the second embodiment of the present invention.

[0065]FIG. 9 shows the circuitry of a noise reducing sharpening circuit adaptable to the video signal processor in accordance with the second embodiment of the present invention. The present embodiment is different from the first embodiment in a point that a reference level for non-correlation detection can be adjusted based on a noise level and that a luminance signal enjoying a good signal-to-noise ratio is not subjected to noise cancellation.

[0066] A noise level detected by a noise level detecting circuit 16 shown in FIG. 9 is communicated to the non-correlation detecting circuit 15. The noise level detecting circuit 16 shown in FIG. 9 detects a noise level dependently on which a threshold voltage based on which the non-correlation detecting circuit 15 detects a non-correlation is varied. Consequently, the non-correlation detecting circuit 15 varies the threshold voltage depending on the noise level, and causes the sharpening circuit to reduce a noise.

[0067]FIG. 10 is a block diagram for explaining the noise level detecting circuit 16 shown in FIG. 9. As shown in FIG. 10, the noise level detecting circuit 16 consists of bandpass filters (BPFS) 101 and 103, an rms value detecting circuit 102, a synchronizing separator 104, a sampling signal generator 105, and a sample-and-hold circuit 106.

[0068] The BPF 101 is used to fetch a mixed noise from a luminance signal Y. Specifically, the BPF 101 limits a signal to be sent to the rms value detecting circuit 102 to the frequencies of a noise. The noise fetched when the BPF 101 limits the luminance signal Y to the frequency band of the noise is transferred to the rms value detecting circuit 102.

[0069] The rms value detecting circuit 102 detects a root-mean-square (rms) value of a received signal, and communicates the rms value in the form of a direct voltage. FIG. 11 is a circuit diagram for explaining an example of the circuitry of the rms value-of-noise detecting circuit 102. As shown in FIG. 11, the rms value-of-noise detecting circuit 102 consists mainly of a multiplier 111 and three operational amplifiers OP1, OP2, and OP3.

[0070] A signal component fetched by the BPF 101 is applied to input terminals X2 and Y1 of the multiplier 111. Output signals of the multiplier 111 are transferred to the operational amplifier OP1 through output terminals W1 and W2. An output signal of the operational amplifier OP1 is applied to an input terminal X1 of the multiplier 111, and sent to the operational amplifier OP2 that is an inverting amplifier. An output signal of the operational amplifier OP2 whose polarity is opposite to the polarity of the input signal is applied to an input terminal Y2 of the multiplier 111.

[0071] A signal whose polarity is opposite to the polarity of an output signal transferred from the multiplier 111 through the output terminal W2 is applied to the input terminal Y2 of the multiplier 111. A signal whose polarity is the same as the polarity of an output signal sent from the multiplier 111 through the output terminal W1 is applied to the input terminal X1 of the multiplier 111.

[0072] Consequently, an output of a circuit composed of the multiplier 111 and operational amplifiers OP1 and OP2 is balanced when an output of the operational amplifier OP1 is zero, and calculated according to formula (1) described below.

(Vin−Vout)×(Vin+Vout)  (1)

[0073] In other words, the output of the circuit composed of the multiplier 11 and operational amplifiers OP1 and OP2 is provided as formula (2) below.

Vout={square root}(|Vin²|)  (2)

[0074] When a sine-wave signal is sent to the rms value-of-noise detecting circuit shown in FIG. 11, a rms value of the input signal is detected as a direct voltage component at the emitter of the transistor Q102. An output signal of the transistor Q102 has the polarity thereof reversed by the operational amplifier OP3, and has the direct voltage component thereof adjusted by resistors R103 and R104. The adjusted direct voltage component, that is, the rms value of the signal sent to the rms value-of-noise detecting circuit shown in FIG. 11 is transferred to the sample-and-hold circuit 106 shown in FIG. 10 through an output terminal OT.

[0075] On the other hand, the BPF 103 shown in FIG. 10 receives the luminance signal Y, passes a predetermined frequency component of the luminance signal Y, and transfers the predetermined frequency component to the synchronizing separator 104. The synchronizing separator 104 separates a vertical sync signal from the received signal, and transfers the vertical sync signal to the sampling signal generator 105.

[0076] The sampling signal generator 105 produces a sampling signal, which represents the portion of the luminance signal having neither a video signal nor a control signal superimposed thereon, with the vertical sync signal sent from the synchronizing separator 104 as a reference signal. FIG. 12A to FIG. 12C show the waveforms of signals for explaining the actions of the synchronizing separator 104 and sampling signal generator 105.

[0077]FIG. 12A shows timing pulses preceding and succeeding the vertical sync signal contained in the luminance signal sent to the synchronizing separator 104. The synchronizing separator 104 separates the vertical sync signal (Vsync) as shown in FIG. 12A. The vertical sync signal shown in FIG. 12A is transferred to the sampling signal generator 105.

[0078] The sampling signal generator 105 uses the vertical sync signal sent from the synchronizing separator 104 as a reference signal, and produces a sampling signal. The sampling signal goes, as shown in FIG. 12C, high at the trailing edge of the vertical sync signal shown in FIG. 12B and remains high during one horizontal scanning period (1H). During the other period, the sampling signal is low.

[0079] The sampling signal generator 105 is realized with, for example, a D flip-flop circuit. A signal of a high logic level into which the vertical sync signal is converted as shown in FIG. 12B is, as shown in FIG. 13, applied to the clear input terminals CLR of D flip-flop circuits 181 and 182. A signal of a high logic level into which a horizontal sync signal is converted is applied to the clock terminals >of the D flip-flop circuits 181 and 182. The active low output terminal (*Q) (where * means active low) of the D flip-flop circuit 181 is connected to the data input terminal (D) of the D flip-flop circuit 182. Consequently, the sampling signal shown in FIG. 12C is provided as an active high output signal (Q) of the D flip-flop circuit 182.

[0080] The sampling signal produced by the sampling signal generator 105 as shown in FIG. 12C is transferred to the sample-and-hold circuit 106. When the sampling signal produced by the sampling signal generator 105 is high, the sample-and-hold circuit 106 samples a signal.

[0081] In the foregoing present embodiment, a period during which the sampling signal is high as shown in FIG. 12C is one horizontal scanning period that is the duration of an equalizing pulse immediately succeeding the vertical sync signal as shown in FIG. 12A. During the period, neither a video signal nor a control signal is superposed on the luminance signal.

[0082] When the sampling signal produced by the sampling signal generator is high, the sample-and-hold circuit 106 samples the rms value detected by the rms value detecting circuit 102. Consequently, the rms value (which may be referred to as a noise level) of the portion of the luminance signal that contains only a noise but does not contain any intelligence signal such as a video signal or a control signal can be detected accurately. The noise level is communicated from the noise level detecting circuit 16 to the non-correlation detecting circuit 15.

[0083] In the second embodiment, the passband of the BPF 101 is the same as that of the BPF 103. Needless to say, the passbands of the BPFs 101 and 103 may be different from each other.

[0084] When the video signal processor in accordance with the second embodiment of the present invention is used to reduce a noise contained in a received video signal, a white noise derived from the presence of a weak electric field can be reduced successfully.

[0085] According to the first embodiment of the present invention, a video signal processor consists mainly of a sharpening circuit and a non-correlation detecting circuit. The sharpening circuit uses a transversal filter to filter a received luminance signal, multiplies the filtered luminance signal by a predetermined factor, adjusts a time lag the luminance signal undergoes in the transversal filter, and adds the resultant luminance signal to an original luminance signal. The non-correlation detecting circuit performs non-correlation detection to discriminate a portion of the luminance signal filtered by the transversal filter, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation. When a received luminance signal portion is detected to contain only a noise by the non-correlation detecting circuit, the sharpening circuit performs noise canceling to subtract the noise from the luminance signal portion. Consequently, owing to the sharpening circuit, despite the simple circuitry, the video signal processor can successfully cancel noises contained in a video signal.

[0086] In the video signal processor in accordance with the first embodiment of the present invention, when the non-correlation detecting circuit judges that a received luminance signal portion has no correlation but contains only a noise, the non-correlation detecting circuit sets the factor for the sharpening circuit to a negative value. When the received luminance signal portion exhibits no fluctuation but contains only a noise, sharpening is suspended and noise reduction is performed in order to cancel the noise. Consequently, noises contained in a received luminance signal can be reduced effectively over a broad frequency band.

[0087] Moreover, in the video signal processor in accordance with the first embodiment of the present invention, when the non-correlation detecting circuit judges that a received luminance signal portion has a correlation, contains a noise, exhibits a fluctuation, the factor for the sharpening circuit is set to a positive value. When the received luminance signal portion exhibits a large fluctuation, the high-frequency component of the luminance signal portion is added to an optical luminance signal portion for enhancement. Consequently, sharpness can be improved by performing ordinary sharpening.

[0088] Moreover, a video signal processing method in accordance with the first embodiment of the present invention consists mainly of sharpening and non-correlation detection. During sharpening, a transversal filter is used to filter a received luminance signal, the filtered luminance signal is multiplied by a predetermined factor, a time lag the luminance signal undergoes in the transversal filter is adjusted, and the resultant luminance signal is added to an original luminance signal. During non-correlation detection, a portion of the luminance signal filtered by the transversal filter, which contains only a noise, is discriminated from a portion thereof that contains a noise and exhibits a fluctuation. When a received luminance signal portion is detected to contain only a noise during the non-correlation detection, noise canceling is performed in order to subtract the noise from the luminance signal portion during the sharpening. Owing to the sharpening, despite the simple processing, the video signal processing method can successfully cancel noises contained in a video signal.

[0089] Moreover, in the video signal processing method in accordance with the first embodiment of the present invention, during the non-correlation detection, when it is judged that a received luminance signal portion has no correlation but contains only a noise, the factor for sharpening is set to a negative value. When the received luminance signal portion exhibits no fluctuation but contains only a noise, sharpening is suspended and noise reduction is performed in order to cancel the noise. Noises contained in the received luminance signal can therefore be effectively reduced over a broad frequency band.

[0090] Moreover, in the video signal processing method in accordance with the first embodiment of the present invention, during the non-correlation detection, when it is judged that a received luminance signal portion has a correlation, contains a noise, and exhibits a fluctuation, the factor for sharpening is set to a positive value. When the received luminance signal portion exhibits a large fluctuation, the high-frequency component of the luminance signal portion is added to an original luminance signal portion for enhancement. Consequently, sharpness can be improved through ordinary sharpening.

[0091] According to the second embodiment of the present invention, a video signal processor consists mainly of a sharpening circuit, a non-correlation detecting circuit, and a noise level detecting circuit. The sharpening circuit uses a transversal filter to filter an input luminance signal, multiplies the filtered luminance signal by a predetermined factor, adjusts a time lag the luminance signal undergoes in the transversal filter, and adds the resultant luminance signal to an original luminance signal. The non-correlation detecting circuit performs non-correlation detection to discriminate a portion of the luminance signal filtered by the transversal filter, which contains only a noise, from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage. The noise level detecting circuit detects a noise level. When a received luminance signal portion is detected to contain only a noise by the non-correlation detecting circuit, the sharpening circuit performs noise reduction to subtract the noise from the luminance signal portion. At this time, the threshold voltage employed in the non-correlation detection by the non-correlation detecting circuit is varied depending on the noise level detected by the noise level detecting circuit. owing to the sharpening circuit, despite the simple circuitry, even if the noise level varies, since the noise level detecting circuit can detect the noise level, the video signal processor can successfully cancel noises which are contained in a video signal and which range from a small-amplitude noise to a large-amplitude noise.

[0092] Moreover, in the video signal processor in accordance with the second embodiment of the present invention, the threshold voltage employed in the non-correlation detection by the non-correlation detecting circuit is dependent on the pre-set noise level. When non-correlation detection is performed continuously, noise reduction can be achieved all the time. Moreover, the luminance signal will not be deteriorated.

[0093] Moreover, in the video signal processor in accordance with the second embodiment of the present invention, the threshold voltage employed in the non-correlation detection by the non-correlation detecting circuit is varied depending on specifications. Therefore, noise reduction can be achieved based on specifications.

[0094] Moreover, according to the second embodiment of the present invention, a video signal processing method consists mainly of sharpening, non-correlation detection, and noise level detection. During sharpening, a transversal filter is used to filter an input luminance signal, the filtered luminance signal is multiplied by a predetermined factor, a time lag the luminance signal undergoes in the transversal filter is adjusted, and the resultant luminance signal is added to an original luminance signal. During non-correlation detection, a portion of the luminance signal filtered by the transversal filter which contains only a noise is discriminated from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage. During noise level detection, a noise level is detected. When a received luminance signal portion is detected to contain only a noise during the non-correlation detection, noise reduction is performed in order to subtract the noise from the luminance signal. At this time, the threshold voltage employed in the non-correlation detection is varied depending on the noise level detected during the noise level detection. Owing to the sharpening, despite the simple processing, even if the noise level is varied, the noise level can be detected during the noise level detection. Consequently, the video signal processing method can successfully cancel noises which is contained in a video signal and which range from a small-amplitude noise to a large-amplitude noise.

[0095] Moreover, in the video signal processing method in accordance with the second embodiment of the present invention, the threshold voltage employed in the non-correlation detection is dependent on the pre-set noise level. Therefore, when non-correlation detection is performed continuously, noise reduction can be achieved all the time. The luminance signal will not be deteriorated.

[0096] Moreover, in the video signal processing method in accordance with the second embodiment of the present invention, during the non-correlation detection, the threshold voltage is varied depending on specifications. Consequently, noise reduction can be achieved based on specifications. 

What is claimed is:
 1. A video signal processor comprising: a sharpening circuit for filtering an input luminance signal using a transversal filter, multiplying the filtered luminance signal by a predetermined factor, adjusting a time lag the luminance signal undergoes in the transversal filter, and adding the resultant luminance signal to an original luminance signal; and a non-correlation detecting circuit for performing non-correlation detection to discriminate a portion of the luminance signal filtered by said transversal filter, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation, wherein when a received luminance signal portion is detected to contain only a noise by said non-correlation detecting circuit, said sharpening circuit performs noise canceling to subtract the noise from the luminance signal.
 2. A video signal processor according to claim 1 , wherein if said non-correlation detecting circuit judges that a received luminance signal portion has no correlation but contains only a noise, said non-correlation detecting circuit sets the factor for said sharpening circuit to a negative value.
 3. A video signal processor according to claim 2 , wherein if said non-correlation detecting circuit judges that a received luminance signal portion has a correlation, contains a noise, and exhibits a fluctuation, said non-correlation detecting circuit sets the factor for said sharpening circuit to a positive value.
 4. A video signal processing method comprising the steps of: sharpening to be performed for filtering an input luminance signal using a transversal filter, multiplying the filtered luminance signal by a predetermined factor, adjusting a time lag the luminance signal undergoes in the transversal filter, and adding the resultant luminance signal to an original luminance signal; and non-correlation detection to be performed for discriminating a portion of the luminance signal filtered by said transversal filter, which contains only a noise, from a portion thereof that contains a noise and exhibits a fluctuation, wherein when a received luminance signal portion is detected to contain only a noise during said non-correlation detection, noise canceling is performed in order to subtract the noise from the luminance signal portion during said sharpening.
 5. A video signal processing method according to claim 4 , wherein if it is judged during said non-correlation detection that a received luminance signal portion has no correlation but contains only a noise, the factor for said sharpening is set to a negative value.
 6. A video signal processing method according to claim 5 , wherein if it is judged during said non-correlation detection that a received luminance signal portion has a correlation contains a noise, and exhibits a fluctuation, the factor for said sharpening is set to a positive value.
 7. A video signal processor comprising: a sharpening circuit for filtering a received luminance signal using a transversal filter, multiplying the filtered luminance signal by a predetermined factor, adjusting a time lag the luminance signal undergoes in the transversal filter, and adding -the resultant luminance signal to an original luminance signal; a non-correlation detecting circuit for performing non-correlation detection to discriminate a portion of the luminance signal filtered by said transversal filter, which contains only a noise, from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage; and a noise level detecting circuit for detecting a noise level, wherein when a received luminance signal portion is detected to contain only a noise by said non-correlation detecting circuit, said sharpening circuit performs noise canceling to subtract the noise from the luminance signal portion, and the threshold voltage employed in the non-correlation detection by said non-correlation detecting circuit is varied depending on the noise level detected by said noise level detecting circuit.
 8. A video signal processor according to claim 7 , wherein the threshold voltage employed in the non-correlation detection by said non-correlation detecting circuit is dependent on the pre-set noise level.
 9. A video signal processor according to claim 8 , wherein the threshold voltage employed in the non-correlation detection by said non-correlation detecting circuit is varied depending on specifications.
 10. A video signal processing method comprising the steps of: sharpening to be performed for filtering an input luminance signal using a transversal filter, multiplying the filtered luminance signal by a predetermined factor, adjusting a time lag the luminance signal undergoes in the transversal filter, and adding the resultant signal to an original luminance signal; non-correlation detection to be performed for discriminating a portion of the luminance signal filtered by said transversal filter, which contains only a noise, from a portion thereof, which contains a noise and exhibits a fluctuation, according to a predetermined threshold voltage; and noise level detection to be performed for detecting a noise level, wherein when a received luminance signal portion is detected to contain only a noise during said non-correlation detection, noise canceling is performed in order to subtract the noise from the luminance signal portion during said sharpening, and the threshold voltage employed in said non-correlation detection is varied depending on the noise level detected during said noise level detection.
 11. A video signal processing method according to claim 10 , wherein the threshold voltage employed in said non-correlation detection is dependent on the pre-set noise level.
 12. A video signal processing method according to claim 11 , wherein the threshold voltage employed in said non-correlation detection is varied depending on specifications. 